Attempts to introduce genes into hematopoietic stem cells (HSCs) have been disappointing. In general, using murine retroviral based vectors to transduce CD34+ cells in vitro have resulted in a low level (0.1-1%) of gene marking for a limited period of time. Studies in canines demonstrated that LTBMC transduced with retroviral vectors gave higher levels of gene marking in vivo. The advantage of this technique is that by using unfractionated marrow there is no preselection; stem cells and retrovirus are able to colocalize on the stroma; the system selects for LTCIC; transduction occurs 3 times over 21 days following feeding so that cells are in cycle, improving transduction efficiency. We examined the utility of this technique in rhesus macaques. In 2 animals that underwent this autologous transplantation procedure, no conditioning regime was implemented. Unfractionated marrow was transduced for 15 - 18 days with a PA317LN based vector. Animals were monitored for "neo" the marker gene in peripheral blood and bone marrow. We observed between 1% and 3% gene marking in peripheral blood for approximately 3 months. The frequency of neo in bone marrow was generally lower than that in peripheral blood. This technique appears encouraging as our data are similar to what has been observed by others, but our protocol is in the absence of any conditioning regimen. Results of these studies may prove useful in efforts to optimize genetic modification of